A ureter is a tubular passageway in a body that carries urine from a kidney to a bladder. Ureteral stents are used to assist urinary drainage from the kidney to the urinary bladder in patients with a ureteral obstruction or injury, or to protect the integrity of the ureter during a variety of surgical manipulations. Stents may be used to treat or avoid ureteral obstructions (such as ureteral stones or ureteral tumors), which disrupt the flow of urine from the kidneys to the bladder. Serious obstructions may cause urine to back up into the kidneys, threatening renal function. Ureteral stents may also be used after endoscopic inspection of the ureter to prevent obstruction of the ureter by swelling of the ureteral wall caused by the surgical procedure.
Ureteral stents typically are tubular in shape and terminate in two opposing ends: a kidney-end and a bladder-end. One or both of the ends may be shaped in a way to prevent the upward and/or downward migration of the stent due, for example, to physiological movements. The ends may be coiled in a pigtail or J-shape to retain their position in the ureter. A kidney-end coil resides within a lumen of the kidney, known as the renal pelvis, and is designed to prevent stent migration down the ureter and into the bladder. Similarly, the bladder-end coil resides in the bladder and is designed to prevent stent migration upward toward the kidney. The bladder coil may also be used to aid in retrieval and removal of the stent.
Regions such as the trigone region in the bladder and the region of the ureter near the bladder known as the ureteral-vesical junction are particularly sensitive and thus prone to irritation by foreign objects. Commonly used bladder-end coils contact and irritate these regions causing discomfort to the patient. Moreover, ureteral stents, particularly the bladder-end, may produce adverse effects including blood in the urine, a continual urge to urinate, and strangury. Thus, while providing drainage from the kidney to the bladder, stents may also cause or contribute to significant patient discomfort and serious medical problems.